In the field of electronic circuit assembly, electronic components are often carried from a supply of such components to a specific location on a circuit board for attachment thereto. The components may be of several different types, one group of which is known as through-hole components. Through-hole components include a body having a plurality of pins projecting therefrom, which are adapted to be inserted through a matching number of apertures on a printed circuit board and soldered on the reverse side of the circuit board to electrically connect and secure the component to the circuit board. The pins of the through-hole component, which are generally formed in at least two aligned rows, project either downwardly from the bottom portion of the body, as shown by the component in FIG. 1 and the angled connector in FIG. 3, or outwardly from the side portions of the body for a first distance and then downwardly for a second distance, as illustrated by the component shown in FIG. 2. Examples of through-hole components include memory chips, resistors, connectors, dual in-line processors (DIPS), and gate arrays. Common to each type of through-hole component are the downwardly projecting terminal ends of the pins, which are adapted to be inserted through the aligned apertures of a printed circuit board.
Rather than manually installing and soldering each individual through-hole component to a circuit board, the electronics industry makes extensive use of robotic placement machines, which grasp a component at a specific location (the supply) and place it at another specific location (the circuit board) with the pins of the component through the apertures in the printed circuit board. Such machines may also be known as insertion machines, because the machine inserts the pins of the component through the apertures in the printed circuit board, where the pins are soldered to the board. To ensure the sustained operation of such robotic placement machines, a continuous supply of electronic components must be furnished to the machine at a predetermined location, in order that the robotic placement machine may be programmed to repeat a precise sequence of movements during every cycle. It is therefore important that each such component be located in the same position (i.e. the point at which the robotic placement machine grasps the component) as each preceding and succeeding component.
One way to provide a continuous supply of electronic components to a desired location is to attach a series of such components at constant intervals to a length of carrier tape. The loaded carrier tape, which is usually provided in roll form, may then be advanced toward the pick-up location at a predetermined rate as each succeeding component is removed from the tape by the robotic placement machine. For example, conventional carrier tape 10 is shown in combination with robotic placement machine 24 in FIG. 4. Supply roll 12 provides carrier tape 10 having an aligned plurality of regularly spaced pockets 14, each of which is loaded with a component (not shown). As shown in FIGS. 5 and 6, conventional carrier tapes generally comprise a lower portion that carries the component, and a flexible cover strip. The cover strip aids in preventing foreign matter from deleteriously affecting the component, and may engage the lower portion periodically, as shown in FIG. 5, or be releasably bonded to the lower portion, (e.g. thermally, ultrasonically or adhesively), as shown in FIG. 6. The cover strip is peeled away from the lower portion just before the robotic placement machine removes the component from the carrier tape.
Referring again to FIG. 4, stripper assembly 16 peels cover strip 18 from the carrier tape around stripper block 20, which block assists in preventing stripper assembly 16 from pulling carrier tape 10 away from its designated path. Carrier tape 10 is advanced by sprocket 22, which engages advancement holes along at least one outer edge of carrier tape 10 to advance carrier tape toward robotic placement machine 24. As each successive component reaches the desired pick-up point, the robotic placement machine grasps the component (either manually or by suction) and places it on a circuit board with the pins of the component inserted through apertures in the circuit board.
An example of a conventional carrier tape for through-hole components is shown in FIG. 5, and is generally similar in design to the carrier tapes shown in U.S Pat. Nos. 4,583,641 (Gelzer) and 4,757,895 (Gelzer). Carrier tape 10a includes substrate 30 including a plurality of holes into which the pins of through-hole component 32 are inserted, usually manually. The pins project beyond substrate 30, and it is therefore desirable to protect the pins from damage. The pins are pressed into and protected by a foam cushion layer 34, which is generally the same width and length as substrate 30, and is thicker than the length of the pins. Cover strip 36 is periodically attached to substrate 30, and assists in protecting through-hole components 32 prior to use. An aligned row of advancement holes formed in substrate 30 is adapted to receive drive sprockets of an advancement mechanism for advancing the carrier tape toward a desired location.
While having its own utility, the carrier tape shown in FIG. 5 may be undesirable because it is typically assembled by hand, which is slow and expensive because it usually requires an extensive commitment of human resources for large scale operations. The substrate, cushion layer, and cover strip configuration is also relatively difficult to assemble, and the use of such packaging is expensive and considered by some to be wasteful. Furthermore, the component is not in a sealed area, and as a result the component is susceptible to dust and other airborne contaminants. The illustrated carrier tape may not include any anti-static capability, and an electrical charge that is applied to the carrier tape may be conducted directly to the component, which may damage the component. Finally, the carrier tape shown in FIG. 5 does not protect the through-hole components mounted thereon from the application of significant pressure to the top of the component. For example, a loaded carrier tape is typically stored and transported in roll form, and the through-hole components carried by the carrier tape described above and located near the core of the roll could be subjected to compressive forces that would damage the components. Similarly, the through-hole components at the outer periphery of the roll could be subjected to impact that would damage the components.
Another type of carrier tape is shown in FIG. 6, and is available from Minnesota Mining and Manufacturing Company of St. Paul, Minn. Carrier tape 10b is a molded polymeric material that includes a strip portion 50 in which a series of pockets 14b have been formed to carry through-hole components 52. Each pocket includes a bottom wall 54 and four side walls 56, and bottom wall 54 further includes channel 58, which is adapted to surround the pins (not shown) projecting from the underside of the through-hole component. Dividers 60 separate adjacent through-hole components, and assist in positioning components 52 within pockets 14b. Strip portion 50 includes two parallel rows of advancement holes 62 and 64, which are dimensioned to be engaged by the teeth of sprocket 66 to convey the carrier tape in direction 70. A cover tape 72, which is releasably bonded to strip portion 50, aids in protecting the through-hole components 52 from airborne contaminants prior to use.
The carrier tape shown in FIG. 6, while overcoming some of the deficiencies of the carrier tape referenced above, also includes some undesirable features. For example, each through-hole component is free to rattle within the confines of pocket 14b, which could damage the pins of the component, or the component itself. The carrier tape also does not organize the through-hole components in the most space efficient manner, which wastes packaging materials.
Most importantly, carrier tapes generally, and the illustrated carrier tape in particular are not intended to convey through-hole components of different sizes. For through-hole components that are larger than those that the pocket would usually contain, the pocket would be too small, which would require a component packager to stock carrier tapes having larger pockets than that packager would normally use. This could require that the packager maintain an increased inventory and incur the concomitant costs thereof. When smaller through-hole components are conveyed on a carrier tape that would normally carry larger components, the smaller components could rattle within the pocket, which could damage the pins of the component. Furthermore, if the component is small enough, any significant displacement would prevent the robotic placement machine from locating and grasping the component because the component would not be presented at the precise location that is required for effective operation of the robotic placement machine. For example, the Electronic Industries Association restricts the maximum allowable rotation of a component in a carrier tape cavity to no more than 20.degree. with respect to the carrier tape, and a relatively slight displacement of a small component could result in an angular rotation that exceeds the limit established by the E.I.A. The carrier tape described above, which may tend to permit translational or rotational movement of smaller components, is thus disadvantageous because it may not present each component in the same location as the previous component.
In view of the disadvantages of the carrier tapes of the prior art, it is therefore desirable to provide a carrier tape for through-hole components that protects the components it conveys, is inexpensive and space efficient, and that can be easily adapted to convey different types and sizes of through-hole components.